Just FYI... my tumblr accounts seem to be checked just fine by X-Notifier in Firefox now (but I have no new messages), so...
Is your account not being checked at all (the account shows up in red or says 'not checked'), or is it simply not showing new messages that are in your inbox?
If that were happening to me, I'd delete the account in X-Notifier, Options... and make sure I had the latest release of the script for Tumblr (currently 2014-08-05) ...then restart the browser, and redefine my tumblr account in X-Notifier, Options with that latest script.
What "doesn't work"?
Just FYI... my tumblr accounts seem to be checked just fine by X-Notifier in Firefox now (but I have no new messages), so...
Is your account not being checked at all (the account shows up in red or says 'not checked'), or is it simply not showing new messages that are in your inbox?
It's not been checked....
It's not been checked....
Troubleshoot
If that were happening to me, I'd delete the account in X-Notifier, Options... and make sure I had the latest release of the script for Tumblr (currently 2014-08-05) ...then restart the browser, and redefine my tumblr account in X-Notifier, Options with that latest script.